Ffordd Pen Llech ([fɔrð pʰɛn ɬeːχ]) is a public road in the town of Harlech which lies within Snowdonia National Park, North Wales.

[6] Whilst this translates to the vertical rise being 36.63% of the horizontal going, it is normal practice for UK highway authorities to round gradients to a nominal figure to avoid confusing road users with excessive precision;[7] hence the warning sign at the top gives a slope of 40%.

To avoid problems with vehicles meeting on the steepest part of the slope and being unable to restart, the lower portion of the road is a one-way descent.

[12] Its popularity is limited by the one-way system requiring downward travel only (UK law treats bicycles as vehicles and requires riders to observe all traffic signs),[13] meaning that a cyclist would have to defy the regulation to attempt the ascent[14] or make the upward journey via the adjacent road, Twtil, which has a shallower gradient of 25%.

[15] YouTuber HubNut (Ian Seabrook) has driven the exact same Australian-built Ford Fairmont (Australia) car down Ffordd Pen Llech in 2023 and Baldwin Street, Dunedin, New Zealand in 2019.